That's a hallucination caused by Mad Hatter. Fox never created the cure during AC. Hatter only made you see what you wanted most.
Also the fighting in AC is much better than in AA. The special takedown which you can use after reaching 8x combo or with upgrade with 5x combo definitely makes you invulnerable to all attacks. I tested it with Titan thug and Abramovic in arena. It's funny actually, I remember having all bats/medals in predator in AA and struggling with the fighting challenges and in AC it's reverse. The armored thugs suck all the fun from predator.
Don't worry about the knife dodge, you'll get used to it and I'm sure you will also learn to take them down with the upgrade, too.